This invention relates to an electrical circuit for use with an electric arc welding system. The circuit is designed so that an operator may momentarily close a switch located on a handheld torch to initiate the welding operation, and he may thereafter release the switch with the welding operation continuing undisturbed. The circuit is failsafe in that it will terminate the welding operation any time the arc is interrupted.
There are two prior art types of systems available which provide a trigger/hold type of circuit of the type described above. The first type uses an alternating relay, or its electronic equivalent, and this circuit merely provides that the first switch closure initiates the welding operation, and the second switch closure will terminate it. One disadvantage of this type of system is that the operator could walk away from the system before terminating the welding operation, and the system would continue to operate, causing serious problems and hazards.
A second type of system utilizes a current sensing relay to latch the system in operation. This type of system overcomes the difficulty mentioned above in that if the operator were to walk away from the system, and the arc interrupted, the welding sequence would be terminated. However, this type of system requires that the arc be terminated in order to discontinue the system, and this normally results in an undesirable length of wire being drawn from the tip of the torch when the operator withdraws the torch from the workpiece to extinguish the arc.